Vibration element, manufacturing method thereof, and vibration wave actuator

ABSTRACT

A vibration element includes a substrate, a piezoelectric element including a piezoelectric layer and an electrode layer, and a bonding layer provided between the piezoelectric element and the substrate and comprising ceramic containing melted glass powder, wherein the vibration element causes the substrate to vibrate by vibration energy of the piezoelectric element to output the vibration energy of the substrate, and the piezoelectric element is fixed to the substrate via the bonding layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.13/118,320 filed May 27, 2011, which claims priority to Japanese PatentApplication No. 2010-124711 filed May 31, 2010, all of which are herebyincorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vibration element in which apiezoelectric element is fixed onto a substrate, a manufacturing methodthereof, and a vibration wave actuator using the vibration element.

2. Description of the Related Art

In a vibration wave actuator, a piezoelectric element has commonly beenused as a vibration source of a vibration element. A single platepiezoelectric element, or a laminated piezoelectric element obtained bystacking many piezoelectric layers and then sintering formed/integratedlayers, is used as the piezoelectric element. Particularly, comparedwith the single plate piezoelectric element, the laminated piezoelectricelement has an advantage of being able to obtain a large deformation ora large force with a low applied voltage due to multi-layering (U.S.Pat. No. 7,109,639).

FIG. 5 is a perspective view of appearance of a linear vibration wave(ultrasonic wave) actuator 30 discussed in U.S. Pat. No. 7,109,639. Thelinear vibration wave actuator 30 includes a vibration element 31 and arod-shaped moving member (linear slider) 36 in pressure contact. Thevibration element 31 includes a laminated piezoelectric element 35 and adrive plate 32 and the laminated piezoelectric element 35 has aplurality of piezoelectric layers and electrode layers stackedalternately. The drive plate 32 is made of metal and is bonded to thelaminated piezoelectric element 35 by an adhesive. The drive plate 32includes a plate portion formed in a rectangular shape and twoprotruding portions 33 a and 33 b formed in a convex shape on a topsurface of the plate portion. The protruding portions 33 a and 33 b havecontact portions 34 a and 34 b, respectively, formed on a tip surfacethereof. The contact portions 34 a and 34 b are members to come directlyinto contact with the linear slider 36 as driven elements and thus havepredetermined wear resistance. The linear vibration wave actuator 30excites two bending vibration modes to cause the protruding portions 33a and 33 b to make an elliptic motion. The elliptic motion generates arelative movement force between the linear slider 36 and the vibrationelement 31, with which the linear slider 36 is in contact underpressure. The linear slider 36 is linearly driven by the relativemovement force.

When the laminated piezoelectric element 35 is manufactured, first agreen sheet to be a piezoelectric layer is produced from piezoelectricmaterial powder and an organic binder by the doctor blade or a similarmethod and then an electrode material paste is printed to predeterminedpositions on the green sheet to produce an electrode layer. Then, apredetermined number of green sheets are stacked in a plane shape andpressurized for lamination. Subsequently, the piezoelectric layer andthe electrode layer are sintered at the same time to integrate thelayers, and polarization is performed to finish the laminatedpiezoelectric element 35 to predetermined dimensions by machining in theend. Also a piezoelectric electrostrictive film actuator having anintegrated laminated structure integrated by heat treatment of anelectrode material and a piezoelectric material alternately stacked in alayered shape on at least one side of the ceramic substrate is known.

FIGS. 6A and 6B illustrate a vibration element 40 integrated bysintering a piezoelectric element 41, including a piezoelectric layer 45and electrode layers 44 and 46, and a ceramic substrate 42, as avibration element, at the same time.

A piezoelectric layer 43 as a compound layer having the same componentsor the same main components as the piezoelectric layer 45 is placedbetween the electrode layer 44 of the piezoelectric element 41 and theceramic substrate 42, and the piezoelectric element 41 and the ceramicsubstrate 42 are joined by sintering (Japanese Patent ApplicationLaid-Open No. 2009-124791).

In the vibration element 31 of the linear vibration wave actuator 30discussed in U.S. Pat. No. 7,109,639, the laminated piezoelectricelement 35 and the drive plate 32 made of metal are bonded by anadhesive made of resin.

However, an adhesive made of resin is relatively soft. Thus, vibrationdamping of a vibration element is large and particularly an influence ofthe vibration damping of a vibration element increases with a decreasingsize thereof, causing degradation of efficiency of a small vibrationwave actuator as a leading factor. Moreover, when the vibration elementis miniaturized, an influence of variations in thickness of an adhesionlayer and accuracy of position due to adhesion on performance of a smallvibration wave actuator increases and also variations of performance ofsmall vibration wave actuators increase.

Further, according to the manufacturing method of a conventionallaminated piezoelectric element, the costs of plant and equipmentinvestment of production units for green sheet formation frompiezoelectric material powder, laminating press, machining and the likeare large, contributing to increasing manufacturing costs as a factor.Thus, like the above piezoelectric electrostrictive film actuator havingan integrated laminated structure, a method of directly fixing alaminated piezoelectric element to a ceramic substrate without providingan adhesion layer with an adhesive at the same time as the production ofthe laminated piezoelectric element is used.

However, a chemical reaction is normally less likely to occur between anelectrode layer of a piezoelectric element and a ceramic substrate,resulting in comparatively low bonding strength between the electrodelayer and the substrate. Thus, the element may peel off from thesubstrate from the start or is more likely to peel off due to vibration.

Therefore, Japanese Patent Application Laid-Open No. 2009-124791proposes the vibration element 40 integrated by sintering after thepiezoelectric layer 43 being placed between the electrode layer 44 ofthe piezoelectric element 41 and the ceramic substrate 42.

However, while it is possible to increase bonding power with the ceramicsubstrate 42 by placing the piezoelectric layer 43 therebetween, thepiezoelectric element 41 may peel off from the ceramic substrate 42 if alarger vibration amplitude is provided to a vibration element. Thus, itbecomes necessary to further increase bonding power between thepiezoelectric element 41 and the ceramic substrate 42.

SUMMARY OF THE INVENTION

The present invention is directed to a vibration element capable ofoutputting stable vibration energy by attempting to improve bondingstrength between a piezoelectric element and a substrate with aninexpensive configuration and improving vibration efficiency by curbingvibration damping accompanying miniaturization, a manufacturing methodthereof, and a vibration wave actuator.

According to an aspect of the present invention, a vibration elementincludes a substrate, a piezoelectric element including a piezoelectriclayer and an electrode layer, and a bonding layer provided between thepiezoelectric element and the substrate and comprising ceramiccontaining melted glass powder, wherein the vibration element causes thesubstrate to vibrate by vibration energy of the piezoelectric element tooutput the vibration energy of the substrate, and the piezoelectricelement is fixed to the substrate via the bonding layer.

According to another aspect of the present invention, a method formanufacturing a vibration element by fixing a piezoelectric elementhaving a piezoelectric layer and an electrode layer to a substrateincludes forming a bonding layer containing glass powder on thesubstrate by using the substrate formed of ceramic or metal, forming thepiezoelectric element on the formed bonding layer, and integrating thesubstrate, the bonding layer, and the piezoelectric element bysimultaneous sintering thereof.

According to yet another aspect of the present invention, a vibrationwave actuator includes the vibration element as a driving power source.

According to an exemplary embodiment of the present invention, avibration element capable of outputting stable vibration energy byattempting to improve bonding strength between a piezoelectric elementand a substrate with an inexpensive configuration and improvingvibration efficiency by curbing vibration damping accompanyingminiaturization, a manufacturing method thereof, and a vibration waveactuator can be realized.

Further features and aspects of the present invention will becomeapparent from the following detailed description of exemplaryembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments, features,and aspects of the invention and, together with the description, serveto explain the principles of the invention.

FIGS. 1A to 1C are block diagrams illustrating a configuration of avibration element according to a first exemplary embodiment of thepresent invention. FIG. 1A is a front view, FIG. 1B is a side view, andFIG. 1C is a plan view.

FIGS. 2A to 2C are block diagrams illustrating the configuration of avibration element according to a second exemplary embodiment of thepresent invention. FIG. 2A is a front view, FIG. 2B is a side view, andFIG. 2C is a plan view.

FIGS. 3A to 3C are block diagrams illustrating the configuration of avibration element according to a third exemplary embodiment of thepresent invention. FIG. 3A is a front view, FIG. 3B is a side view, andFIG. 3C is a plan view.

FIG. 4 is a diagram illustrating a drive mechanism of a linear vibrationwave actuator into which the vibration element according to the first tothird exemplary embodiments of the present invention is incorporated.

FIG. 5 is a diagram illustrating the configuration of a conventionallinear vibration wave actuator.

FIGS. 6A and 6B are diagrams illustrating the configuration of aconventional vibration element.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the inventionwill be described in detail below with reference to the drawings.

A configuration example of a vibration element according to a firstexemplary embodiment of the present invention will be described withreference to FIGS. 1A to 1C. FIGS. 1A to 1C are a front view, a sideview, and a plan view of the vibration element, respectively. FIG. 1Billustrates a section in a broken line position indicated by arrows inFIG. 1C.

A vibration element 1 a illustrated in FIGS. 1A to 1C is assumed to beapplied to a linearly driven vibration wave actuator. The vibrationelement 1 a includes a substrate 2 in a plate shape, a piezoelectricelement 15, and a bonding layer 3. As described below, the substrate 2and the piezoelectric element 15 are bonded (fixed) and integrated bysimultaneous sintering. That is, the piezoelectric element 15functioning as a vibration energy source and the substrate 2 functioningas a vibration element that accumulates the vibration energy are fixedand integrated via the bonding layer 3. In the piezoelectric element 15,an electrode layer 4, a piezoelectric layer 5, an electrode layer 6, anda piezoelectric layer 7 are sequentially stacked. The electrode layer 4is divided into two portions and the divided portions are arranged in aspaced state. Similarly, the electrode layer 6 is divided into twoportions and the divided portions are arranged in a spaced state.

The piezoelectric layer 5 covers the entire surface of the electrodelayer 4, and the piezoelectric layer 7 covers the entire surface of theelectrode layer 6. Electric conduction between the electrode layers 4and 6 and external portions (such as a control unit) is realized byforming a hole 8 in the piezoelectric layers 5 and 7 and introducing aconductive wire 9 onto the electrode layers 4 and 6 via the hole 8 tofix the conductor wire 9 to solder or the like. Alternatively, athrough-hole filled with a conductor may be formed in the hole 8 torealize conduction to the conductor wire.

An alternating signal is supplied to the electrode layers 4 and 6 fromthe control unit that controls the vibration of the piezoelectricelement 15, and the piezoelectric layer 5 expands and contracts(distortion) due to the alternating signal so that the expansion andcontraction is output to the outside as vibration energy. The substrate2 vibrates due to the vibration energy, and the vibration of thesubstrate 2 is used as a driving force to drive a driven element (see alinear slider 14 in FIG. 4).

The substrate 2 has a length of 12 mm, a width of 5 mm, and a thicknessof 0.3 mm. The thickness of the bonding layer 3 is about 6 μm, thethickness of the piezoelectric layer 5 is about 12 μm, the thickness ofthe piezoelectric layer 7 is about 6 μm, and the thickness of theelectrode layers 4, 6 is about 5 μm. The hole 8 for conduction has adiameter of 1 mm.

Next, the manufacturing method of the vibration element 1 a will bedescribed.

First, alumina (aluminum oxide) that is sintered ceramic in a plateshape is ground and cut to finish the substrate 2 to predetermineddimensions. Next, a piezoelectric material paste prepared by mixingpiezoelectric material powder, glass powder, and an organic vehicle madeup of an organic solvent and an organic binder and containing glasspowder capable of forming a thick film is applied to the surface on oneside of the ceramic plate by screen printing. Then, the organic solventis removed by heating the applied piezoelectric material pastecontaining glass powder at about 150° C. for 10 min to dry the paste toform the bonding layer 3. Then, a conductive material paste is preparedby mixing conductive material powder containing silver and palladium asmain components and an organic vehicle made up of an organic solvent andan organic binder. The conductive material paste is applied onto thedried bonding layer 3 by screen printing, and the paste is dried byheating at about 150° C. for 10 min to form the electrode layer 4.

Next, a piezoelectric material paste prepared by mixing piezoelectricmaterial powder and an organic vehicle made up of an organic solvent andan organic binder and capable of forming a thick film is applied to thesurface of the electrode layer 4 by screen printing. Then, the organicsolvent is removed by heating the applied piezoelectric material pasteat about 150° C. for 10 min to dry the paste to form the piezoelectriclayer 5. By repeating the application and drying in this manner, theelectrode layer 6 and the piezoelectric layer 7 are formed.

The piezoelectric material powder used to form the bonding layer 3 haslead zirconate and lead titanate (PbZrO₃—PbTiO₃) having a perovs kitecrystal structure as main components. Moreover, three-component ormulti-component piezoelectric material powder prepared by adding anddissolving a small amount of a compound made of a plurality of metals isused. The same piezoelectric material powder is used for thepiezoelectric layers 5 and 7.

Further, silicon oxide and boron oxide are contained as the glass powderand in addition, an additive such as bismuth oxide, alumina, alkalimetal oxide, alkali earth metal oxide, and other metallic oxide is mixedand formulated so that a glass softening point appropriate for a burningtemperature is achieved.

Then, glass powder (also called glass frit) prepared by pulverizingglass once melted into an average grain size of 1 to 2 μm is used. Theglass powder is added by 0.2% to several percentage points by weight ofthe piezoelectric material powder to prepare a paste.

By changing the mixing ratio of silicon oxide and boron oxide, thesoftening point of glass can be changed. Also, the reaction with thesubstrate 2 can be increased by selecting the additive element.

The piezoelectric material powder of the bonding layer 3 is sinteredduring sintering and the glass powder softens and flows to gather in therespective interfaces of the substrate 2 and the electrode layer 4 sothat the bonding layer 3 can strongly be bound to the substrate 2 andthe electrode layer 4.

The piezoelectric layer 5 sandwiched between the electrode layers 4 and6 is a layer that causes a displacement according to the applied voltageas a piezoelectric active portion with polarization treatment. Thebonding layer 3 and the piezoelectric layer 7, on the other hand, arenot piezoelectric active portions and instead, piezoelectric inactiveportions that do not actually cause a displacement.

Incidentally, the piezoelectric layers 5 and 7 and the bonding layer 3may be compounds in which the mixing ratio of main components of leadzirconate and lead titanate (PbZrO₃—PbTiO₃) is changed or componentsother than the main components are changed. In addition, the thicknessof the piezoelectric layers 5 and 7 and the thickness of the bondinglayer 3 may be made different.

A paste prepared by adding piezoelectric material powder by 10% byweight in advance in addition to a conductive material is used as theconductive material paste to form the electrode layers 4 and 6.

However, the same effect can be obtained if the piezoelectric materialpowder to be added contains the same components as those of thepiezoelectric layer 5 or the same lead zirconate and lead titanate(PbZrO₃—PbTiO₃) as the main components. The piezoelectric layers 5 and 7have a plate of screen printing worked with in advance so that the hole8 (unprinted portion) can be formed and the electrode layers 4 and 6 areeach divided into two portions via the unprinted portion to be arrangedby being spaced.

The bonding layer 3, the piezoelectric layers 5 and 7, and the electrodelayers 4 and 6 stacked alternately on the substrate 2 in this manner arein an unsintered state.

After the organic binder being removed first by heating using a furnaceat temperature of 500° C. or below, the laminated layer is sintered inan atmosphere of lead at the highest temperature of 1100° C. in aretention time of two hours. That is, the bonding layer 3, thepiezoelectric layers 5 and 7, the electrode layers 4 and 6, and thesubstrate 2 are sintered at the same time and integrated. In otherwords, the manufacture of a piezoelectric element and bonding (fixing)of the piezoelectric element and the substrate 2 occurred at the sametime.

The bonding layer 3 made of ceramic is provided to bond the substrate 2and the electrode layer 4. Silver and palladium forming the electrodelayer 4 and used as conductive materials have weak bonding power withthe substrate 2. Thus, if there is no bonding layer 3, the electrodelayer 4 may be peeled off from the substrate 2 from the start, or theelectrode layer 4 of the piezoelectric element 15 is more likely to beseparated from the substrate 2 due to vibration.

The piezoelectric material powder of the bonding layer 3 whose maincomponents are the same as those of the piezoelectric material is mostdesirable in terms of the thermal expansion coefficient, mechanicalproperties, and costs, but the powder material may have componentssimilar to those of the substrate, in addition to those of thepiezoelectric material.

In the present exemplary embodiment, for example, alumina powder mixedwith glass powder may be used. Particularly, alumina is easily availableand inexpensive, has high heat resistance, and is less likely tochemically react with other materials and thus, alumina powder havingglass powder mixed therewith is appropriate.

If alumina is used for the substrate described below, above all, aluminais a material of the same kind and is more likely to bond throughdiffusion, making alumina suitable for bonding with the substrate.

Other material powder that can be sintered at the same time when thepiezoelectric element is sintered during sintering can be used.

The electrode layer 4 uses conductive material powder made of noblemetals containing silver as a main component and palladium by about 20%to 30% by weight of the whole powder. Thus, the electrode layer 4 startsto sinter at a lower temperature than the bonding layer 3 and thepiezoelectric layer 5 and contraction caused by sintering is large sothat a more compact layer is formed. Thus, melted glass is present onlybetween the substrate 2 and the electrode layer 4, and there is almostno diffusion or penetration into the piezoelectric layer 5.

If glass diffuses or penetrates into the piezoelectric layer 5,piezoelectric characteristics of the piezoelectric layer 5 normallydeteriorate and thus, the electrode layer 4 can prevent glass fromdiffusing or penetrating into the piezoelectric layer 5. Moreover, theforce of peeling off from the bonding layer 3 or the piezoelectric layer5 is made smaller by mixing piezoelectric powder in the electrode layer4 to curb contraction caused by sintering of the conductive materialpowder.

As the material of the substrate 2, on the other hand, alumina, whichis, as described above, sintered ceramic in a plate shape, is selectedas a preferable material for the substrate as a vibration element.Compared with other ceramics, alumina is easily available andinexpensive. Moreover, vibration damping is relatively smaller whenalumina is used as a vibration element.

However, mechanical strength deteriorates and vibration damping as avibration element grows when purity thereof becomes lower and thus,alumina of higher purity is more desirable. Alumina is rather brittle asa mechanical component and so a small amount of other components may beadded. For example, zirconia oxide can improve mechanical strength andelectric insulation properties and so can be an additive. In this case,as discussed in Japanese Patent Application Laid-Open No. 2006-74850,zirconia oxide can be added by 5 to 40% by weight.

Any material that forms stable bonding with the bonding layer 3 havingglass powder mixed therewith in advance may be used for the substrate 2.In addition to alumina, zirconia, silicon carbide, and silicon nitride,which are normal ceramics, but can easily bond to the substrate becauseglass powder is mixed in the bonding layer 3 in advance, can be used forthe substrate. It is desirable to consider additive elements in additionto silicon oxide and boron oxide as glass powder components by fittingto various kinds of ceramics.

Further, the bonding layer 3 functions as a buffer of stress generateddue to contraction when the substrate 2, the electrode layers 4 and 6,and the piezoelectric layers 5 and 7 are sintered or a difference ofthermal expansion coefficients when the temperature drops aftersintering so that an effect of preventing peeling of the substrate 2 andthe electrode layer 4 is gained. When the vibration element vibrates,the bonding layer 3 functions also as a buffer for the substrate 2 ofstress generated due to a displacement of the piezoelectric layer 5acting as a piezoelectric active layer.

What is different from the conventional configuration is the use of thebonding layer 3 mixed with glass powder, whereby particularly glassmolten solid material melted by sintering increases strength of closecontact between the substrate 2 and the electrode layer 4 so thatbonding power between the substrate 2 and the electrode layer 4 can beincreased.

The piezoelectric layer 5 covers the electrode layer 4 and thepiezoelectric layer 7 covers the electrode layer 6, and particularly theelectrode layers 4 and 6 are completely covered up to edges thereof sothat the electrode layers 4 and 6 are not exposed to the surface asprotective layers of insulation properties. By providing the protectivelayers of the electrode layers 4 and 6 with the piezoelectric layers 5and 7 in this manner, peeling of the electrode layers 4 and 6 caused bya mechanical force from outside can be prevented.

Moreover, peeling of the electrode layers 4 and 6 can be prevented bypreventing, for example, a short circuit when foreign matter comes intocontact, a current leak at high humidity, and infiltration of moistureinto a gap between the electrode layers 4 and 6 and the piezoelectriclayers 5 and 7.

After, as described above, the bonding layer 3, which is ceramic, thepiezoelectric layers 5 and 7, the electrode layers 4 and 6, and thesubstrate 2 being sintered at the same time and integrated, theconductor wire 9 is bonded to the electrode layers 4 and 6 via the hole8 of the piezoelectric layers 5 and 7 using solder or the like and avoltage is applied between the electrode layers 4 and 6 to performpolarization of the piezoelectric layer 5.

Polarization is performed under polarization conditions of applying apredetermined voltage of about 35 V (corresponding to 3 KV/mm) betweenthe grounded (G) electrode layer 4 and the positive (+) electrode layer6 in oil at temperature of 120 to 150° C. for about 30 min.

Pastes to form the bonding layer 3, the piezoelectric layers 5 and 7,and the electrode layers 4 and 6 are created by adding a small amount ofadditives and kneading an organic vehicle using an organic binder suchas ethyl cellulose and an organic solvent such as terpineol using athree-roll mill.

While the thickness of a piezoelectric layer is set to 12 μm for screenprinting in the present exemplary embodiment, piezoelectric layers andelectrode layers whose thickness ranges from about 2 to 3 μm to 30 μmcan be created with high precision. Divided electrodes and piezoelectriclayers with a hole (unprinted portion) can be provided in a plate.Compared with lamination by the green sheets described above, the screenprinting cannot only forma thinner and more precise film easily, butalso control an application position with high precision without theneed of machining after sintering.

Further, manufacturing equipment becomes more inexpensive. As a resultof the above, the manufacturing cost also becomes more inexpensive.

A configuration example of a vibration element according to a secondexemplary embodiment of the present invention will be described withreference to FIGS. 2A to 2C. FIGS. 2A to 2C are a front view, a sideview, and a plan view of the vibration element, respectively. FIG. 2Billustrates a section in a broken line position indicated by arrows inFIG. 2C.

While there is one piezoelectric layer sandwiched by electrode layers inthe first exemplary embodiment, there are two piezoelectric layerssandwiched by electrode layers in the present exemplary embodiment. Thatis, compared with the first exemplary embodiment, a laminatedpiezoelectric element 16 in the present exemplary embodiment has onepiezoelectric layer and one electrode layer added thereto. In otherwords, in the second exemplary embodiment, the voltage is made lowerthan in the first exemplary embodiment by increasing the layers to twopiezoelectric layers acting as piezoelectric active portions.

The voltage can further be lowered by increasing the layers to three ormore piezoelectric layers which are piezoelectric active portions.

In a vibration element 1 b according to the present exemplaryembodiment, the bonding layer 3, the electrode layer 4, a piezoelectriclayer 5 a, an electrode layer 6 a, a piezoelectric layer 5 b, anelectrode layer 6 b, and the piezoelectric layer 7 are sequentiallystacked as the laminated piezoelectric element 16 on the sinteredsubstrate 2 in a plate shape.

The piezoelectric layer 5 a wholly covers the electrode layer 4, thepiezoelectric layer 5 b wholly covers the electrode layer 6 a, and thepiezoelectric layer 7 wholly covers the electrode layer 6 b. Theelectrode layers 4 and 6 b realize electric conduction through a hole 10filled with a conductive paste (conductive material), and electricconduction to an external power supply can be established by theconductor wire 9 bonded to a hole 11. The electrode layer 6 a canestablish electric conduction to the outside (such as a control unit)via the conductor wire 9 bonded to a hole 12 filled with a conductivepaste.

In the vibration element 1 b, for example, the substrate 2 has thelength of 12 mm, the width of 5 mm, and the thickness of 0.3 mm. Thethickness of the ceramic layer 3 is about 6 μm, the thickness of thepiezoelectric layers 5 a and 5 b is about 12 μm, the thickness of thepiezoelectric layer 7 is about 6 μm, and the thickness of the electrodelayers 4, 6 a, and 6 b is about 5 μm. The diameter of the holes 10 and11 is 1 mm in consideration of wiring. In the present exemplaryembodiment, the piezoelectric layers 5 a and 5 b become piezoelectricactive portions.

In contrast to the first exemplary embodiment, the holes 10, 11, and 12are filled with the conductive paste having almost the same componentsas the conductive paste forming the electrode layers 4, 6 a, and 6 b. Inthis case, after the holes 10, 11, and 12 being formed, the holes 10,11, and 12 are filled with the conductive paste by the screen printingor the like before or after the electrode layers 4, 6 a, and 6 b areformed, and the substrate 2 is sintered simultaneously with thelaminated piezoelectric element 16 for integration.

According to another manufacturing method, after the laminatedpiezoelectric element 16 being sintered, the holes 10, 11, and 12 may befilled with a conductive paste mixed with a heat-hardening adhesive andconductive powder.

FIG. 4 is a diagram illustrating the configuration of a linear vibrationwave actuator into which the vibration element 1 a according to thefirst exemplary embodiment or the vibration element 1 b according to thesecond exemplary embodiment is incorporated.

The principle of linear driving is the same as that in a conventionalexample. The vibration element 1 a or the vibration element 1 b isprovided with a protruding portion 13.

The linear slider 14 under pressure comes into contact with theprotruding portion 13 and the linear slider 14 moves due to an ellipticmotion excited in the protruding portion 13 by the vibration of thepiezoelectric element 15 or 16. That is, the linear vibration waveactuator makes a reciprocating motion of the linear slider 14 using thepiezoelectric element 15 or 16 as a driving power source.

Incidentally, the present invention is not limited to the configurationsof the first exemplary embodiment and the second exemplary embodimentand, for example, while a conductor wire is used for conduction betweenelectrode layers and an external power supply, a flexible circuit boardor a conductive paste may be used to establish electric conductionbetween electrode layers and the external power supply, instead of theconductor wire.

A configuration example of a vibration element according to a thirdexemplary embodiment of the present invention will be described withreference to FIGS. 3A to 3C. FIGS. 3A to 3C are a front view, a sideview, and a plan view of the vibration element, respectively. FIG. 3Billustrates a section in a broken line position indicated by arrows inFIG. 3C.

A vibration element 1 c illustrated in FIGS. 3A to 3C is assumed to beapplied to a linearly driven vibration wave actuator.

The vibration element 1 c includes a substrate 2-2 and a piezoelectricelement 15-2 in a plate shape. Materials of the substrate and apiezoelectric element are different from those in the first exemplaryembodiment. The substrate 2-2 and the piezoelectric element 15-2 arebonded (fixed) and integrated by, as described above, simultaneoussintering.

That is, the piezoelectric element 15-2 functioning as a vibrationenergy source and the substrate 2-2 functioning as a vibration elementthat accumulates the vibration energy are fixed and integrated via abonding layer 3-2.

In the piezoelectric element 15-2, an electrode layer 4-2, apiezoelectric layer 5-2, an electrode layer 6-2, and a piezoelectriclayer 7-2 are sequentially stacked.

The electrode layer 4-2 is divided into two portions, and the dividedportions are arranged in a spaced state. Similarly, the electrode layer6-2 is divided into two portions, and the divided portions are arrangedin a spaced state. The piezoelectric layer 5-2 covers the entire surfaceof the electrode layer 4-2, and the piezoelectric layer 7-2 covers theentire surface of the electrode layer 6-2. Electric conduction betweenthe electrode layers 4-2 and 6-2 and external portions (such as acontrol unit) is realized by forming a hole 8-2 in the piezoelectriclayers 5-2 and 7-2 and introducing a conductive wire 9-2 onto theelectrode layers 4-2 and 6-2 via the hole 8-2 to fix the conductor wire9-2 with solder or the like. An alternating signal is supplied to theelectrode layers 4-2 and 6-2 from the control unit that controls thevibration of the piezoelectric element 15-2, and the piezoelectric layer5-2 expands and contracts (distortion) due to the alternating signal sothat the expansion and contraction is discharged to the outside asmechanical vibration energy. The substrate 2-2 vibrates due to thevibration energy, and the vibration of the substrate 2-2 is used as adriving force to drive a driven element (see the linear slider 14 inFIG. 4).

The substrate 2-2 has the length of 12 mm, the width of 5 mm, and thethickness of 0.3 mm. The thickness of the bonding layer 3-2 is about 6μm, the thickness of the piezoelectric layer 5-2 is about 12 μm, thethickness of the piezoelectric layer 7-2 is about 6 μm, and thethickness of the electrode layers 4-2 and 6-2 is about 5 μm. The hole8-2 for conduction has a diameter of 1 mm.

Next, the manufacturing method of the vibration element 1 c will bedescribed.

First, martensitic stainless steel (SUS420J2), which is excellent invibration characteristics and easy to machine, is ground and cut tofinish the substrate 2-2 to predetermined dimensions. Next, apiezoelectric material paste prepared by mixing piezoelectric materialpowder, glass powder, and an organic vehicle made up of an organicsolvent and an organic binder and containing glass powder capable offorming a thick film is applied to the surface on one side of thesubstrate 2-2 by screen printing. Then, the organic solvent is removedby heating the applied piezoelectric material paste containing glasspowder at about 150° C. for 10 min to dry the paste to form the bondinglayer 3-2.

Piezoelectric material powder prepared by adding a small amount ofcompound made of one or a plurality of metallic elements to bariumtitanate (BaTiO₃) as the main component is used as the piezoelectricmaterial powder of the bonding layer 3-2.

Silicon oxide and boron oxide are contained as the glass powder and inaddition, bismuth oxide, alumina, alkali metal oxide, and alkali earthmetal oxide are mixed. Then, glass powder (also called glass frit)prepared by pulverizing glass once melted into an average grain size of1 to 2 μm is used. The glass powder is added by 0.2% to severalpercentage points by weight of the piezoelectric material powder toprepare a paste.

By changing the mixing ratio of silicon oxide and boron oxide, thesoftening point of glass can be changed. Also by selecting the additiveelement, reactions with the substrate can be increased. Then, aconductive material paste is prepared by mixing conductive materialpowder made of silver and an organic vehicle made up of an organicsolvent and an organic binder.

The conductive material paste is applied onto the dried bonding layer3-2 by screen printing and the paste is dried by heating at about 150°C. for 10 min to form the electrode layer 4-2. Silver in the conductivematerial powder may contain a slight amount of platinum or palladium.

Next, a piezoelectric material paste prepared by mixing piezoelectricmaterial powder, glass powder as a sintering assistant, and an organicvehicle made up of an organic solvent and an organic binder and capableof forming a thick film is applied to the surface on one side of thesubstrate by screen printing. Then, the organic solvent is removed byheating the applied piezoelectric material paste at about 150° C. for 10min to dry the paste to form the piezoelectric layer 5-2.

A piezoelectric material prepared by adding a small amount of compoundmade of one or a plurality of metallic elements to barium titanate(BaTiO₃) as the main component is used for the piezoelectric layer 5-2.The sintering temperature of barium titanate (BaTiO₃) is normally highand thus, glass powder as a sintering assistant is mixed in the presentexemplary embodiment so that the piezoelectric layers 5-2 and 7-2 can besintered at 700° C. The glass powder as a sintering assistant is siliconoxide or boron oxide that is basically the same as the glass powdermixed in the bonding layer 3-2, but it is desirable to preventdeterioration of piezoelectric characteristics when possible byappropriately selecting the mixing ratio or additive elements thereof.

By repeating the application and drying in this manner, the electrodelayer 6-2 and the piezoelectric layer 7-2 are formed.

If glass powder is mixed with piezoelectric material powder, originalpiezoelectric characteristics generally deteriorate due to involvementof a glass phase having no ferroelectricity (piezoelectricity), but acertain level of piezoelectric characteristics is present and thus,glass powder can be used under conditions where inclusion of lead is notdesirable.

The piezoelectric layer 5-2 is a layer that causes a displacement as apiezoelectric active portion on which polarization is performed and itschemical composition directly affects performance of a vibration waveactuator. On the other hand, the bonding layer 3-2 and the piezoelectriclayer 7-2 are not piezoelectric active portions and instead,piezoelectric inactive portions.

As will described below, at least the piezoelectric element 15-2 isformed of the piezoelectric layer 7-2 as an inactive portion on the sideopposite to the side fixed to the substrate 2-2.

Components other than the main component of barium titanate (BaTiO₃) ofthe piezoelectric layer 5-2, and the bonding layer 3-2, and thepiezoelectric layer 7-2 can be changed to fit each purpose. Moreover,the thickness of the piezoelectric layer 5-2 and the thickness of thebonding layer 3-2 and the piezoelectric layer 7-2 may be made different.

A conductive material paste prepared by adding barium titanate powder by10% by weight in addition to a conductive material is used to form theelectrode layers 4-2 and 6-2. A similar effect is obtained ifpiezoelectric material powder to be added has the same component as thatof the piezoelectric layer 5-2 or the main component thereof is the samebarium titanate.

The piezoelectric layers 5-2 and 7-2 have a plate of screen printingworked with in advance so that the hole 8-2 (unprinted portion) can beformed and the electrode layers 4-2 and 6-2 are each divided into twoportions via the unprinted portion to be arranged in a spaced state. Aplurality of the bonding layer 3-2, the piezoelectric layers 5-2 and7-2, and the electrode layers 4-2 and 6-2 stacked alternately on thesubstrate 2-2 in this manner is in an unsintered state.

After the organic binder being removed by heating using a furnace attemperature of 500° C. or below, the laminated layer is sintered in theatmosphere at temperature 700° C. That is, the bonding layer 3-2, thepiezoelectric layers 5-2 and 7-2, the electrode layers 4-2 and 6-2, andthe substrate 2-2 are sintered at the same time and integrated. In otherwords, the manufacture of a piezoelectric element and bonding (fixing)of the piezoelectric element and a substrate occurred at the same time.

The bonding layer 3-2 is provided to bond the substrate 2-2 and theelectrode layer 4-2.

Silver forming the electrode layer 4-2 and used as a conductive materialhas weak bonding power with the substrate 2-2. Thus, if there is nobonding layer 3-2, the electrode layer 4-2 may be peeled off from thesubstrate 2-2 from the start due to contraction caused by powdersintering when conductive material powder is sintered and thermalexpansion after the sintering is more likely to peel off due tovibration of the piezoelectric element 15-2.

Material powder whose main component is the same as that of thepiezoelectric material is desirable for the bonding later 3-2 in termsof the thermal expansion coefficient and mechanical properties, but inaddition to the piezoelectric material, the material powder may bealumina powder in which glass powder is mixed. Above all, alumina isappropriate because alumina has a thermal expansion coefficient similarto the thermal expansion coefficients of stainless steel and bariumtitanate described above and is less likely to react with othermaterials.

Other ceramic powder that can be sintered at the same time whenpiezoelectric elements are sintered during sintering can be used.

By mixing piezoelectric powder in the electrode layer 4-2 in advance,contraction caused by sintering of the conductive material powder iscurbed to weaken a peeling force.

Further, glass powder is mixed in the bonding layer 3-2 in advance andthe glass powder melts and gathers in the respective interface of thesubstrate 2-2 and the electrode layer 4-2 during sintering so that thebonding layer 3-2 can strongly be bound to the substrate 2-2 and theelectrode layer 4-2 after sintering.

As the metal of the substrate 2-2, on the other hand, in addition to theabove stainless steel, other chrome or chromium-nickel stainless steelmay be selected as a further preferable material of the substrate(vibration element). This is because such metals of all metals areeasily available and inexpensive, has high heat resistance, andvibration damping as a vibration element is small.

Compared with ceramic, stainless steel has oxide formed on the surfacethereof and so stable bonding is likely to be formed with the bondinglayer 3-2 in which glass powder is mixed in advance so that bondingoccurs easily.

Further, thermal expansion coefficients of barium titanate, alumina, andstainless steel are close and can be used.

The bonding layer 3-2 functions also as a buffer of stress generatedduring vibration so that peeling of the substrate 2-2 and the electrodelayer 4-2 can be prevented.

Like in the first exemplary embodiment, the piezoelectric layer 5-2covers the electrode layer 4-2, the piezoelectric layer 7-2 covers theelectrode layer 6-2, and particularly the electrode layers 4-2 and 6-2are completely covered up to edges thereof, so that the electrode layers4-2 and 6-2 are not exposed to the surface as protective layers ofinsulation properties.

By providing the protective layers of the electrode layers 4-2 and 6-2with the piezoelectric layers 5-2 and 7-2 in this manner, peeling of theelectrode layers 4-2 and 6-2 caused by a mechanical force from outsidecan be prevented.

Moreover, peeling of the electrode layers 4-2 and 6-2 can be preventedby preventing, for example, a short circuit when foreign matter comesinto contact, a current leak at high humidity, and infiltration ofmoisture into a gap between the electrode layers 4-2 and 6-2 and thepiezoelectric layers 5-2 and 7-2.

As described above, the bonding layer 3-2, the piezoelectric layers 5-2and 7-2, the electrode layers 4-2 and 6-2, and the substrate 2-2 aresintered at the same time and integrated. Then, the conductor wire 9-2is bonded to the electrode layers 4-2 and 6-2 via the hole 8-2 of thepiezoelectric layers 5-2 and 7-2 using solder or the like, and a voltageis applied between the electrode layers 4-2 and 6-2 to performpolarization of the piezoelectric layer 5-2.

Polarization is performed under polarization conditions of applying apredetermined voltage of about 35 V (corresponding to 3 KV/mm) betweenthe grounded (G) electrode layer 4-2 and the positive (+) electrodelayer 6-2 in oil at temperature 80° C. for about 30 min.

FIG. 4 is a diagram illustrating the configuration of a linear vibrationwave actuator into which the vibration element 1 c according to thepresent exemplary embodiment is incorporated.

According to the exemplary embodiments of the present invention, asdescribed above, glass powder is used for bonding so that the presentinvention can be applied to a variety of substrates and a variety ofpiezoelectric materials, enabling an occurrence of stable bonding power.Moreover, the manufacturing cost becomes more inexpensive.

Such configurations of the exemplary embodiments of the presentinvention are useful for development of vibration actuators in thefuture.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures, and functions.

What is claimed is:
 1. A vibration element, comprising: a substrate; apiezoelectric element including a piezoelectric layer and an electrodelayer; and a bonding layer provided between the piezoelectric elementand the substrate and comprising ceramic containing glass, wherein theelectrode layer is fixed to the substrate via the bonding layer, whereinthe bonding layer comprises a compound whose main component is the sameas a main component of the piezoelectric layer, wherein a firstconcentration of the glass at an interface of the substrate and thebonding layer is greater than a second concentration of glass at acenter of the bonding layer, wherein a third concentration of glass atan interface of the bonding layer and the electrode layer is greaterthan the second concentration, and wherein the piezoelectric layer doesnot contain glass defused from the bonding layer.
 2. The vibrationelement according to claim 1, wherein silicon oxide and boron oxide arecontained in the glass and also an additive is added to the glass. 3.The vibration element according to claim 1, wherein the main componentis a piezoelectric material.
 4. The vibration element according to claim1, wherein the substrate comprises ceramic or metal.
 5. The vibrationelement according to claim 4, wherein the ceramic forming the substrateincludes alumina or ceramic prepared by adding zirconia to alumina as amain component.
 6. The vibration element according to claim 4, whereinthe metal forming the substrate is stainless steel.
 7. The vibrationelement according to claim 1, wherein the piezoelectric layer compriseslead zirconate and lead titanate as main components, and wherein theelectrode layer comprises silver and palladium as main components. 8.The vibration element according to claim 1, wherein the piezoelectriclayer comprises barium titanate as a main component, and wherein theelectrode layer comprises silver as a main component.
 9. The vibrationelement according to claim 1, wherein the piezoelectric elementcomprises the piezoelectric layer and the electrode layer beingalternately stacked.
 10. A vibration wave actuator, comprising thevibration element according to claim 1 as a driving power source. 11.The vibration element according to claim 1, wherein the vibrationelement causes the substrate to vibrate by vibration energy of thepiezoelectric element to output the vibration energy of the substrate.12. The vibration element according to claim 1, wherein material for theelectrode layer is different from material for the substrate.
 13. Thevibration element according to claim 1, wherein material for the bondinglayer is different from any one of material for the electrode layer andmaterial for the substrate.